SCREEN FOR SEPARATING SOLIDS FROM DRILLING FLUID

Abstract: A screen (1) for separating solids from drilling fluids comprises an outer frame (2) and a plurality of support members (7, 8, 9, 10, 11). A sheet (19) of perforate material is bonded to both the outer frame (2) and the support members (7, 8, 9, 10, 11) and three layers of mesh (24, 25, 26) are bonded to the sheet (19). In use, the screen (1) is secured in a vibratory shaker. Preferred embodiments have a high life expectancy and high conductance. Furthermore, accidental damage can be contained and repaired if desired.

Description: SCREEN FOR SEPARATING SOLIDS FROM DRILLING FLUID This invention relates to a screen for separating solids from drilling fluid, a vibratory shaker fitted with such a screen and a sheet of perforate material for use in said screen. Drilling fluid is used to maintain the tip of a drill cool and to carry solids to the surface of the wellbore. Once at the surface the solids are removed from the drilling fluid which is reused. One piece of apparatus commonly used to separate the solids from the drilling fluid is a vibratory sha¬ ker. Vibratory shakers generally comprise a frame which, in use, oscillates back and forth. Shortly before use a screen is unrolled and placed on the frames. The screen remains in place until it fails at which time the screen is replaced. Because of the highly abrasive nature of the solids in drilling fluid the life of the screen is relatively short. In order to increase screen life manufacturers have resorted to the use of screens fabricated from large diameter threads which are interwoven to form a grid. Whilst this prolongs screen life (typically 2 - 3 days) the conductance (volumetric throughput) of the screen is severely restricted. In an attempt to increase conductance it has been proposed to fabricate a screen from a perforated plate to which was bonded a sheet of relatively fine mesh. This solution provided excellent conductance. However, the screens themselves were extremely delicate and often needed replacement every 1-2 days. It should be noted that in both the above embodi¬ ments the screen is simply unrolled and placed on the frame before use. The aim of at least preferred embodiments of the present invention is to provide a screen which has a relatively high conductance and a relatively high work¬ ing life. According to the present invention there is provi¬ ded a screen for separating solids from drilling fluid, which screen is characterized in that it comprises an outer frame, at least one support member extending across said outer frame, a sheet of perforate material secured to said outer frame and said support member, and at least one sheet of mesh secured to said sheet of perforate material. Preferably, a plurality of support members extend across said outer frame and said sheet of perforate material is secured to each. This has quite remarkable advantages. In particular, in a preferred embodiment the screen had a typical life of from 7 to 10 days. Preferably, the support members are disposed at centres between 140 and 170 mm. The present invention also has a further signif¬ icant advantage. In particular, if a prior art screen was inadvertently pierced, for example by dropping a tool on the screen, the damage would quickly spread over the entire screen rendering it useless in a matter of minutes. In contrast, with screens in accordance with the present invention the damage can be confined between adjacent support members or between a support member and the frame. Such a small area can rapidly be patched albeit at the cost of some throughput. In order to help ensure that all the contaminated drilling fluid which is introduced onto the screen is treated generally uniformly, the sheet preferably com¬ prises two sets of ribs which are inclined to opposite sides of said at least one support member. Typically, said ribs will intersect at an angle of from 20° to 90°, and preferably 60°. Advantageously, said sheet includes transverse ribs which extend across said screen generally perpendicular to said support members and which pass through the intersection of said ribs of said two sets of ribs. Another aspect of the present invention provides a vibratory shaker fitted with a screen in accordance with the invention. The present invention also provides in or for use in a screen according to the present invention, a sheet of perforate material comprising two edges and two sets of ribs which are inclined to one another and to said edges and at least one sheet of mesh secured thereto. Preferably, said ribs intersect at an angle of from 20° to 90°. Advantageously, said edges are provided with mem¬ bers for attaching the sheet to a vibratory shaker. For a better understanding of the invention refer¬ ence will now be made, by way of example, to the accom¬ panying drawings, in which:- Figure 1 is a perspective view showing the bottom of one embodiment of a screen in accordance with the present invention; Figure 2 is a partially cut away top plan view of the screen shown in Figure 1; Figure 3 is a bottom plan view of a second embodiment of a screen in accordance with the present invention; and Figure 4 is a top plan view, to an enlarged scale, of part of the screen encircled and identified by the reference letter "A" in Figure 3. Referring to the drawings, there is shown a screen which is generally identified by reference number 1. The screen 1 comprises an outer frame 2 which is generally rectangular and comprises four frame members 3, 4, 5 and 6. The frame member 3 and 5 are each 107cm (42.35 inches) long whilst the frame members 4 and 6 are each 74cm (29 inches) long. All the frame members 3, 4, 5, 6 have a 2.54cm x 2.54cm (1 inch x 1 inch) cross-section. Five support members 7, 8, 9, 10, 11 extend between the frame members 3 and 5 and define six bays 12, 13, 14, 15, 16, 17 of equal width. A rod 18 extends from the frame member 4 to the frame member 6 and is attached to each of the support members 7, 8, 9, 10 and 11 to maintain them properly spaced from one another. A sheet 19 of perforate material is bonded to the frame members 3, 4, 5, 6 and the support members 7, 8, 9, 10, 11. The sheet 19 is made from steel and comprises a plurality of square holes 20 which are each 2.54cm x 2.54cm (1 inch x 1 inch). The square holes 20 are ar- ranged in rows, for examples rows 21, 22, 23. The square holes 20 in each row 21, 22, 23 are separated by approx¬ imately 3mm (1\8 inch) and the rows 21, 22, 23 them¬ selves are separate by approximately 3mm (1/8 inch). The square holes in alternate rows are aligned with one another but are offset from the square holes in adjacent rows as shown. The upper surface of the sheet 19 is covered with an adhesive and a first sheet of mesh 24 is bonded thereto. If desired further sheets of mesh 25, 26 may be bonded to the sheet 19 at the same time as the first sheet of mesh 24. Typically, the mesh 23, 24, 25 will have from 40 to 270 openings per linear inch (16 to 106 openings per linear cm) with 60 to 180 openings per linear inch (24 to 71 openings per linear cm) being more usual. In use, several screens 1 are simply laid between the side rails in the base of a vibratory shaker and secured in place. The vibratory shaker is then set in motion. When contaminated drilling fluid is introduced onto the screens the drilling fluid passes through the screens whilst the solids are retained on the screen in the usual manner. The screens are normally inclined by a few degrees so that the solids travel to the lower end of the screen and fall into a hopper for disposal or further processing. It should be noted that the screens 1 are arranged so that their support members 7, 8, 9, 10 and 11 extend along the vibratory shaker in the direct of travel of the solids.. It will be appreciated that existing vibratory shakers are provided with support beams which are welded in place. Ideally these should be removed to obtain full conductance. However, we have found that the screens 1 may simply be laid over the support beams if desired. Various modifications to the embodiment described are envisaged. For example, whilst the sheet 19 is preferably bonded to the frame members, 3, 4, 5, 6 and the support members 7, 8, 9, 10, 11 it could also be secured by, for example continuous welding, spot weld- ing, rivets and screws. Turning again to Figure 2, it has been found that, in use, contaminated drilling fluid tends to move line¬ arly along the screen 1 with little movement transverse to the direction of vibration. As a result, with the exception of when it passes over the metal strips be¬ tween the rows 21, 22; 22,23 some contaminated drilling fluid is nearly always over a square hole. In contrast, a small proportion of the drilling fluid is only over a square hole for part of the time. In particular, the small proportion which passes over the ribs between the rows 21, 22; 22, 23 and over the ribs between adjacent squares in the same row. Although this problem is parti¬ ally mitigated by offsetting the squares in alternate rows as disclosed in Figures 1 and 2, the situation is not entirely satisfactory. The screen shown in Figures 3 and 4 addresses this problem. In Figures 3 and 4 parts having similar func¬ tion to parts shown in Figures 1 and 2 have been given the same reference numerals increased by 100. As shown in Figures 3 and 4 a plurality of triangu¬ lar openings 127, 128, 129, 130 are punched out of the sheet 119. The triangular openings 127, 128 are arranged in rows 121, 122, 123. Adjacent triangular openings 127, 128 in each row are inverted relative to one another whilst the triangular openings 128 and 129 in adjacent rows 121, 122 are arranged so that either their bases 133 or their apices 134 contact one another. This con¬ struction results in the formation of rows of diagonal ribs 131 and 132 which are inclined to opposite sides of the support members 107, 108 and which intersect one another at an angle α of approximately 60°. It will be noted that the bases 133 of the trian¬ gles extend across the screen 101 and form traverse ribs 135 which are generally perpendicular to the support members 107, 108. In use, contaminated drilling fluid passes over the screen 101 in the direction of the arrows D. It will be appreciated that the contaminated drilling fluid is above one or other triangular opening for much of the time whilst it traverses the screen 101. Various modification to the arrangement shown in Figures 3 and 4 are envisaged, for example the angle could vary from 20° to 90°. In addition, the bases 133 could conceivably be dispensed with although this would significantly weaken the sheet 119. The ribs 131, 132 in each set of ribs are preferably equally inclined to opposite sides of the support members 107, 108 although this is not absolutely essential. It would also be possible for the sheet 119, toge¬ ther with layer(s) of mesh 124 to be sold in sheets or in rolls for use in conventional vibratory shakers. When sold for use in conventional vibratory shakers opposite edges of the sheet 119 may be provided with members for attaching the sheet 119 to the vibratory shaker. Such members may be, for example of [-shape cross-section.

Claims: CLAIMS 1. A screen (1) for separating solids from drilling fluid, which screen is characterized in that it com¬ prises an outer frame (2), at least one support member (7, 8, 9, 10, 11) extending across said outer frame (2), a sheet (19) of perforate material secured to said outer frame (2) and said support member (7, 8, 9, 10, 11), and at least one sheet of mesh (24, 25, 26) secured to said sheet (19) of perforate material. 2. A screen as claimed in Claim 1, characterized in that a plurality of support members (7, 8, 9, 10, 11) extend across said outer frame (2) and said sheet (19) of perforate material is secured to each. 3. A screen as claimed in Claim 2, wherein said sup- port members (7, 8, 9, 10, 11) are disposed at centres between 140 and 170 mm. 4. A screen as claimed in any preceding Claim, charac¬ terized in that said sheet (119) comprises two sets of ribs (131, 132) which are inclined to opposite side of said at least one support member (107, 108). 5. A screen as claimed in Claim 4, characterized in that said ribs (131, 132) intersect at an angle α of from 20° to 90°. 6. A screen as claimed in Claim 5, characterized in that angle α is 60°. 7. A screen as claimed in Claim 4, 5 or 6, character¬ ized in that said sheet (119) includes transverse ribs which extend across said screen (101) generally perpen¬ dicular to said support members (107, 108) and which passes through the intersection of said ribs of said two sets of ribs (131, 132). 8. A vibratory shaker fitted with a screen (1) as claimed in any preceding Claim. 9. In or for use in a screen as claimed in Claim 1, a sheet of perforate material comprising two edges and two sets of ribs (131, 132) which are inclined to one an¬ other and to said edges, and at least one sheet of mesh secured thereto. 10. A sheet as claimed in Claim 9, wherein said ribs (131, 132) intersect at an angle α of from 20° to 90°. 11. A sheet as claimed in Claim 9 or 10, wherein said edges are provided with members for attaching the sheet (119) to a vibratory shaker. * * *

Inventors: DUGAL ROBERT L, LEONE VINCENT D SR, WALKER JEFFREY E, DUGAL, ROBERT, L., LEONE, VINCENT, D., SR., WALKER, JEFFREY, E.
Applicants: DUGAL ROBERT L, ENVIRONMENTAL PROCEDURES INC, LEONE VINCENT D SR, LUCAS BRIAN RONALD, WALKER JEFFREY E, DUGAL, ROBERT, L., ENVIRONMENTAL PROCEDURES, INC., LEONE, VINCENT, D., SR., LUCAS, BRIAN, RONALD, WALKER, JEFFREY, E.
Application year: 1994
Main classification: B07B1
IPC codes: B01D29, B01D33, B07B1, E21B21